Want to Win a Bike Race? Hack Your Rival’s Wireless Shifters

Professional cycling has, in its recent history, been prone to a shocking variety of cheating methods and dirty tricks. Performance-enhancing drugs. Tacks strewn on race courses. Even stealthy motors hidden inside of wheel hubs.

Now, for those who fail to download a software patch for their gear shifters—yes, bike components now get software updates—there may be hacker saboteurs to contend with, too.

At the Usenix Workshop on Offensive Technologies earlier this week, researchers from UC San Diego and Northeastern University revealed a technique that would allow anyone with a few hundred dollars of hardware to hack Shimano wireless gear-shifting systems of the kind used by many of the top cycling teams in the world, including in recent events like the Olympics and the Tour de France. Their relatively simple radio attack would allow cheaters or vandals to spoof signals from as far as 30 feet away that trigger a target bike to unexpectedly shift gears or to jam its shifters and lock the bike into the wrong gear.

The trick would, the researchers say, easily be enough to hamper a rival on a climb or, if timed to certain intense moments of a race, even cause dangerous instability. “The capability is full control of the gears. Imagine you’re going uphill on a Tour de France stage: If someone shifts your bike from an easy gear to a hard one, you’re going to lose time,” says Earlence Fernandes, an assistant professor at UCSD’s Computer Science and Engineering department. “Or if someone is sprinting in the big chain ring and you move it to the small one, you can totally crash a person’s bike like that.”

Here’s a video demonstration of the researchers’ hacking technique:

The researchers’ technique exploits the increasingly electronic nature of modern high-end bicycles, which now have digital components like power meters, wireless control of fork suspensions, and wireless shifters. “Modern bicycles are cyber-physical systems,” the researchers note in their Usenix paper. Almost all professional cyclists now use electronic shifters, which respond to digital signals from shifter controls on the bike’s handlebars to move a bicycle’s chain from gear to gear, generally more reliably than mechanical shifting systems. In recent years, those wired electronic shifters have transitioned again to wireless versions that pair via a radio connection, such as the popular Di2 wireless shifters sold by the Japanese cycling component firm Shimano, which the researchers focused on.

To exploit those wireless components and sabotage a specific target bike, the researchers’ technique does require that a hacker first intercept the target’s gear-shift signals at some point before they carry out their attack. The hacker can then replay those signals—even months later—to cause the bike to shift at the hacker’s command.

To carry out that eavesdrop-and-replay attack, the researchers used a $1500 USRP software-defined radio, an antenna, and a laptop. They say though that a $350 HackRF would work just as well, and point out that their hardware setup could be miniaturized to the degree that it could be hidden along the sidelines of a race, in a cycling team car, or even in the back pouch of a rider’s jersey, such as by implementing it in a Raspberry Pi mini-computer.

Jamming wireless shifters with that toolkit would be considerably easier than even replay attacks, the researchers say. While a jamming attack could prevent a specific rider from shifting gears if a hacker were able to first pick up one of their wireless shifting signals, a saboteur could also simply broadcast a jamming signal at the frequency used by all Shimano shifters, potentially disrupting a large group of racers. The researchers even say that it would be possible to read the shifting signals from an entire peloton of cyclists and then jam everyone except a chosen rider. “You can basically jam everyone except you,” says Northeastern professor Aanjhan Ranganathan, another author of the paper.

Shimano’s Di2 wireless shifting components and the researchers’ hacking toolkit. They say their hardware could easily be miniaturized, by using a Raspberry Pi mini-computer for instance, to make it small enough to be hidden along the sidelines of a race, in a cycling team car, or even in the back pouch of a rider’s jersey.Courtesy of UCSD and Northeastern University

The researchers first reached out to Shimano about their research in March, and the company’s engineers worked with them closely to develop a patch. A Shimano spokesperson wrote in a statement to WIRED that the company “identified and created a new firmware update to enhance the security of the Di2 wireless communication systems.”

Shimano says it has provided that firmware update to the professional cycling teams that use its components. But it says its fix won’t be more widely available until late August and declined to explain exactly how its update prevents the attacks the researchers identified. “We can share that this update is intended to improve wireless transmission across Shimano Di2 component platforms," the company writes. “We cannot share details on the exact fix at this moment, for obvious security reasons.”

Exactly how the patch will be deployed to customers isn’t quite clear either. The company writes that “riders can perform a firmware update on the rear derailleur” using Shimano’s E-TUBE Cyclist smartphone app. But it fails to mention whether the fix will apply to the front derailleur. “More information about this process and steps riders can take to update their Di2 systems will be available shortly,” it concludes.

While Shimano’s patching plan leaves a week or two-week gap between the researchers’ public presentation of their bike-hacking technique at Usenix and the broad rollout of a fix for customers, UCSD professor Fernandes argues it’s unlikely that average riders will be targeted with their technique—at least not immediately. “I find it hard to believe that someone will want to launch such an attack on me during my Saturday group ride,” Fernandes says.

Professional cyclists, however, should be sure to implement the early patch that Shimano has already provided, the researchers say. They note, too, that other brands of wireless shifters may be vulnerable to similar hacking techniques: They focused on Shimano only because it has the largest market share.

In the ruthless world of competitive cycling, which has been rocked to its foundations in recent decades by doping scandals, they argue that rivals hacking each others’ shifters is not at all a far-fetched scenario. “This is, in our opinion, a different kind of doping,” says Fernandes. “It leaves no trace, and it allows you to cheat in the sport.”

More broadly, they argue that their radio-based bike hacking research is a cautionary tale about the temptation to add wireless electronic features to every technology, from garage doors to cars to bicycles, and the unintended consequences of that long-term trend—namely, that they’ve all become vulnerable to forms of replay and jamming attacks of the kind that Shimano is now scrambling to fix.

“This is a repeating pattern,” says Northeastern’s Ranganathan, who has also developed solutions for replay attacks on cars’ keyless entry systems. “When manufacturers start putting in wireless features in their products, it has an impact on real-world control systems. And that can cause real physical harm.”

Corrected at 8/14/2024 at 10:00 am ET to note the correct software-defined radio used in the researchers’ experimental setup and remove an incorrect reference to Bluetooth.